Title: Observation Constraints of the End of Reionization
1 Observation Constraints of the End of
Reionization
- Xiaohui Fan
- University of Arizona
Collaborators Becker, Carilli, Ferrara,
Gallerani, Jiang, Richards, Roy Choudhury,
Strauss, Xu, Walter, White, et al.
Background 46,420 Quasars from the SDSS Data
Release Three
2 The Highest Redshift Quasars Today
- z4 1000 known
- z6 19
- SDSS i-dropout Survey
- Completed in June 2006
- 7700 deg2, zAB
- 27 luminous quasars at 5.71
- CFHT High-z Quasar Survey (CFHTQS, Willott et al.
astro-ph/0706091) - Goal 400 deg2, zAB
- 4 quasars at z6
- New highest-z quasar at z6.43
- SDSS Faint Quasar Survey (SFQS)
- faint quasars in the deep SDSS stripe (Jiang, XF
et al.), - 300 deg2, zAB
- six z6 quasar at 20
- Goal quasar LF
- Other on-going z6 quasar surveys
- AGES (Cool et al.) Spitzer selected, one quasar
at z5.8 - FIRST-Bootes (Becker et al.) radio selected, one
quasar at z6.1 - QUEST i-dropout surveys similar to SDSS
- IR-based survey UKIDSS, (z5.83), VISTA, allows
detection up to z8-9.
3(No Transcript)
4Quasar Density at z6
- From SDSS i-dropout survey
- Density declines by a factor of 40 from between
z2.5 and z6 - Cosmological implication
- MBH109-10 Msun
- Mhalo 1012-13 Msun
- rare, 5-6 sigma peaks at z6 (density of 1 per
Gpc3) - Assembly of supermassive BHs?
- The universe is only 20 teddington old,
requiring non-stop Eddington accretion of 100
Msun from z20 - Is Eddington-limited accrection from stellar
seeds still permitted, or are alternative
accretion modes (super-Eddington, intermediate
mass BH) needed?
Fan et al. 2006
5 The Lack of Evolution in Quasar Emission Line
Properties
z6 composite
Ly a
Low-z composite
NV
OI
SiIV
Ly a forest
Fan et al.2007
- Rapid chemical enrichment in quasar vicinity
- Quasar env has supersolar metallicity no
metallicity evolution - High-z quasars are old, not yet first quasars..
6Quasar Metallicity at z6
near-IR spectroscopy Gemini Keck
Jiang, XF et al. 2007
7reionization
- Two Key Constraints
- WMAP 3-yr zreion10/-3
- 2. IGM transmission zreion 6
From Avi Loeb
8End of Reionization EpochOpen Questions
- Whats the Status of IGM at z6?
- Measurements of Gunn-Peterson optical depth
- Evolution of UV background
- Constraints on IGM neutral fraction
- Was the Universe mostly neutral by z6-8?
- Distribution of dark gaps
- HII region size distribution
- Evolution of Lyman alpha emitters
- What is the source of reionization?
- First galaxies or AGNs
9Searching for Gunn-Peterson Trough
- Gunn and Peterson (1965)
- It is observed that the continuum of the source
continues to the blue of Ly-a ( in quasar 3C9,
z2.01) - only about one part of 5x106 of the total mass
at that time could have been in the form of
intergalactic neutral hydrogen - Absence of G-P trough ? the universe is still
highly ionized at z6
10Keck/ESI 30min exposure ?
Gunn-Peterson Trough in z6.28 Quasar
Keck/ESI 10 hour exposure ?
White et al. 2003
11Evolution of Lyman Absorptions at z5-6
?z 0.15
12Accelerated Evolution at z5.7
- Optical depth evolution accelerated
- z
- z5.7 ? (1z)11
- End of reionization?
- Dispersion of optical depth also increased
- Some line of sight have dark troughs as early as
z5.7 - But detectable flux in 50 case at z6
- End of reionization is not uniform, but with
large scatter
(1z)11
(1z)4.5
XF et al. 2006
13Evolution of Ionization State
UV background
- UV Ionizing background
- Assuming photoionization and model of IGM density
distribution - UV background declines by close to an order of
magnitude from z5 to 6.2 - Increased dispersion suggests a highly
non-uniform UV background at z5.8
Neutral fraction
- From GP optical depth measurement, volume
averaged neutral fraction increase by order of
magnitude from z5.5 to 6.2
XF et al. 2006
14Relation between optical depth and neutral
fraction highly model-dependent
- Becker et al. (2006)
- optical depth evolution could be consistent with
a smooth evolution of ionizing background for a
strongly-evolving log-normal density distribution
of the IGM
- Relation between ? and ? dependent on IGM
clumpiness - Simulation results clumpiness 5 - 30, no
strong evolution at z6 - Optical depth evolution driven by an decreasing
background towards high-z
Becker et al. 2006
15Evolution of Proximity Zone Size Around Quasars
Shapiro, Haiman, Mesinger, Wyithe, Loeb et al.
- Size of Proximity Zone region
- Rp (LQ tQ / fHI )1/3
- Size of quasar proximity zone decreases by a
factor of 2.4 between z5.8 and 6.4 (Fan et al.
2006) - Consistent with neutral fraction increased by a
factor of 15 over this narrow redshift range - Can be applied to higher z and fHI with lower S/N
data - Actual size of proximity zone dependent on
details of radiative transfer and quasar model
Proximity zone size (Mpc)
XF et al. 2006
redshift
16Uncertainties in interpretation of proximity zone
sizes
- Bolton Haehnelt (2006), Maselli et al. (2006)
- Observed size of proximity zone much smaller than
true HII region size - Neutral fraction
- Consistent with G-P constraints
- Mesinger et al. (2004), Wyithe et al. (2005)
- Neutral fraction 10-30
- Better models and simulated spectra needed
Maselli et al. 2006
Bolton Haehelt 2006
17CFHTQS results (Willott et al. 2007)
- Strong evolution in ?GP seen at z5.5, but low
S/N - Scaled near-zone size 6-11 Mpc at z6
- Consistent with a low fHI
- But uncertainties in zem based on Ly?
- Caution using Ly? redshift could introduce large
uncertainty in HII region size but true
systematic redshift difficult for faint quasars
at z6
18Dark Gap Distributions
- Dark gap statistics (Songaila Cowie 2002)
- Gaps regions where all pixels have ?2.5
- Gaps among z6 quasars
- Average length shows the most dramatic increase
at z5.8 ? IGM is dominated by long, dark gaps - Consistent with overlap at z6-8?
- Dispersions
- Even at z6, gap lengths are still finite
- Upper limit on neutral fraction
- If IGM largely neutral, GP damping wing will wipe
out all HII region transmissions - Existence of transmission at z6 places an upper
limit of average neutral fraction
et al. 2007) - Independent upper limit on neutral fraction
XF et al. 2006
19Dark Gap Statistics Comparison with Simulations
- Gallerani et al. (2006, 2007)
- Early reionization (zoverlap 15)
- Late reionization (zoverlap 7)
- Significant difference in gap distribution at z6
- fHI
- But observed transmission peaks too wide compared
to simulations
Distribution of width of transmission peaks
Distribution of dark gaps
5.7
6.0
20Ly ? Galaxy LF at z6
Iye et al. 2006 Kashikawa et al. 2006
- Neutral IGM has extended GP damping wing ?
attenuates Ly ? emission line - New Subaru results
- Declining density at z6-7 (2-3? result)
- Reionization not completed by z6.5
- Neutral fraction could be as high as a few tenths
but strongly model-dependent - cf. Malhotra Rhoads, Hu et al. lack of
evolution in Ly ? galaxy density
21GRBs as Probes of Reionization
Damping wing?
GRB050904
- Detected to z6.30
- Advantages
- Bright
- Flat K-correction due to time dilation at high-z
- Small surrounding HII regions could use damping
wing of Gunn-Peterson trough to probe high
neutral fraction
- Constraining neutral fraction
- How to distinguish internal absorption from IGM
damping wing?? - Using 050904 fHI DLA and IGM profiles
Kawai et al. 2005
22What Ionized the Universe? AGNs or Galaxies
Density of quasars
SFR of galaxies
- Quasar LF at z6
- SDSS Wide 7700 deg2, 17 quasars, zAB
- SDSS Deep 150 deg2, 6 quasars, 20
- AGES 1 quasar in 5 deg2 at zAB
- Steeppening of LF
- ??L-3.1
- Comparing to ??L-2.4 at z4
Jiang, XF et al. 2007
23 Reionization by AGNs?
- Can quasars do it?
- Too few quasars unless QLF remains to be steep to
AGN luminosity - Can low-luminosity AGNs ionize the IGM by z6?
- Stacking X-ray image of LBGs in UDF too few
faint AGNs - Can accretion to seed BHs ionize the IGM by z15?
- Dijkstra, Haiman Loeb (2004)
- Soft X-ray background overproduced if quasars
produce 10 photons/H atom - Preionization to f(HI)50 by X-rays is still
allowed (e.g. Ricotti et al.)
Jiang, XF et al. 2007
24Summary
- IGM evolution accelerated at z6
- Neutral fraction increased by order of mag from
z5.5 to z6 - fHI a few percent, but highly model-dependent
- z6 marks the end of overlapping stage of an
inhomogeneous reionization - z6 quasars are old lots of BH build-up and
chemical enrichment at high-z - AGN not likely sources of reionization
25Probing Reionization History
WMAP
26Surveys of quasars at z7
LBT LBC-Red i-z-Y selection (1 deg2/night)
UKIDSS YJHK photometry